1. Field of the Invention
The present invention relates to a charge transporting material useful as organic electronic device materials such as an electrophotographic photoreceptor, an organic EL device, and an organic solar cell and a process for the preparation of charge transporting fine particles used for the material.
2. Description of the Related Art
A low-molecular dispersion type organic semiconductor in which a low-molecular charge transporting compound, such as a triarylamine or tetraarylbenzidine type compound, is dispersed in a resin, or an organic semiconductor containing a charge transporting resin typified by a polyvinyl carbazole derivative (PVK) is an important component of a charge transporting layer in an organic electronic device such as an electrophotographic photoreceptor, an electrophotographic photoconductive toner or an organic EL device. Various proposals have been made with a view to improve the charge transporting ability and physical and chemical durability thereof.
For example, charge transporting resins having as a pendant a charge transporting substituent such as hydrazone or triarylamine have been investigated from the viewpoints of the improvement in charge transporting ability and mechanical durability. Among them, a charge transporting resin having a tetraarylbenzidine skeleton is known to have a high mobility and therefore have high utility as reported in "The Sixth International Congress on Advances in Non-impact Printing Technologies, p.306(1990)".
A polycarbonate or polyester of an arylamine having a specific fluorene skeleton is disclosed in U.S. Pat. No. 5,034,296, and a polyurethane is disclosed in U.S. Pat. No. 4,983,482.
As an example of an organic electronic device using such a charge transporting compound, a heterogeneous electron transporting layer comprising charge transporting molecular crystallites and an insulating resin or a heterogeneous electron transporting layer comprising a block copolymer composed of an insulating block and a charge transporting block, in order to form a contorted charge transporting path in a charge transporting layer as a photoreceptor constitution aimed at obtaining a high image quality for digital image formation in the recent electrophotographic field is proposed in Japanese Patent Application Laid-Open (JP-A) No. 6-83077. However, properties such as charge transporting ability and residual potential of some charge transporting molecules are not always satisfactory in practical use. It has also been proposed to provide a heterogeneous charge transporting layer obtained by dispersing, in an insulating resin, a charge mobile organic pigment such as phthalocyanine or a charge mobile inorganic pigment such as selenium. That proposal was, however, not always satisfactory in practice due to a deviation of charge transferring properties attributable to the heterogeneous particle shape or limitation of the freedom of the device designing in the selection of the charge generating layer, since the pigment has an optical sensitivity in its specific wavelengths.
In order to reduce residual potential or to maintain image quality over a long period, it has been proposed to provide a layer containing a charge transporting compound such as an organic electron transporting pigment (Japanese Patent Application Laid-Open (JP-A) No. 64-3671), a fluorene derivative (Japanese Patent Application Laid-Open (JP-A) No. 2-203352) and a diphenoquinone derivative (Japanese Patent Application Laid-Open (JP-A) 4-353861), each having an electron transporting property, as an undercoat layer for an electrophotographic photoreceptor. For practical use, compounds having even better properties in charge transporting and durability are being sought. Ideally, it is preferred from the viewpoint of heightening the freedom of device designing, to form an undercoat layer as a charge mobility layer to permit the structural control of charge mobility.
On the other hand, application of a low-molecular charge transporting material to an organic EL device has drawn attention. It is however accompanied by the problem that since the low-molecular compound is melted by the joule heat generated when it is applied to an organic EL device, a stable device with a long life is not easily available.